There have been proposed a number of photoelectromotive force members having a photoelectric conversion layer composed of a non crystalline material containing silicon atoms as the main component, namely the so called amorphous silicon (hereinafter referred to as "a-Si") for use in photovoltaic devices and the like.
There have also been proposed various methods for the preparation of such a photoelectric conversion layer using vacuum evaporation, thermo chemical vapor deposition, plasma chemical vapor deposition, reactive sputtering, ion plating and photo chemical vapor deposition techniques.
Among those methods, the method using plasma vapor deposition (hereinafter referred to as "plasma CVD method") has been generally recognized as being the most preferred and is currently used to manufacture the photoelectric conversion layer.
However, for any of the known photoelectric conversion layers, even if it is an acceptable one that is obtained by the plasma CVD method and exhibits fairly satisfactory characteristics, there still remain problems unsolved with respect to obtaining totally satisfactory characteristics, particularly electric and optical characteristics, photoconductive characteristics, deterioration resistance upon repeated use and use environmental characteristics, its homogeneity, reproducibility, mass-productivity, and its long term stability and durability, which are required for the photoelectric conversion layer to be a stable one.
The reasons for the above are largely due to the fact that the photoelectric conversion layer cannot be easily prepared by a simple layer deposition procedure; rather great skill is required in the process operations in order to obtain a desirable photoelectric conversion layer while having due concern for the starting materials.
For example, in the case of forming a film composed of an a-Si material according to the thermo chemical vapor deposition technique (hereinafter referred to as "CVD method"), after the gaseous material containing silicon atoms is diluted, appropriate impurities are introduced thereinto and the thermal decomposition of related materials is carried out at an elevated temperature between 500.degree. and 650.degree. C. Therefore, in order to obtain a desirable a-Si film by the CVD method, precise process operation and control are reguired, and because of this the apparatus in which the process according to the CVD method is practiced becomes complicated and costly. However, even in that case, it is extremely difficult to reproducibly obtain on an industrial scale a desirable homogeneous photoelectric conversion layer composed of an a-Si material having practically applicable characteristics.
Now, although the plasma CVD method is widely used nowadays as above mentioned, it is still accompanied with problems relating to process operations and capital investment.
Regarding the former problems, the operating conditions to be employed under the plasma CVD method are much more complicated than the known CVD method, and it is extremely difficult to generalize them.
That is, there already exist a number of variations even in correlated parameters concerning the temperature of the substrate, the amount and flow rate of gases to be introduced, the degree of pressure and the high frequency power for forming the layer, the structure of the electrodes, the structure of the reaction chamber, the flow rate of gases to be exhausted, and the plasma generation system. Besides said parameters, there also exist other kinds of parameters. Under these circumstances, in order to obtain a desirable deposited film product it is required to choose precise parameters from a great number of variables. And sometimes serious problems occur. For instance, because of the precisely chosen parameters, a plasma is apt to be in an unstable state which causes problems in the deposited film.
Also, the structure of the apparatus in which the process using the plasma CVD method is practiced will eventually become complicated since the parameters to be employed are precisely chosen as above stated. Whenever the scale or the kind of the apparatus to be used is modified or changed, the apparatus must be so structured as to cope with the precisely chosen parameters.
In this regard, even if a desirable deposited film should be fortuitously mass-produced, the film product becomes unavoidably costly because (1) a heavy investment is firstly necessitated to set up a particularly appropriate apparatus therefor; (2) a number of process operation parameters still exist even for such apparatus and the relevant parameters must be precisely chosen from the existing various parameters for the mass-production of such films. In accordance with such precisely chosen parameters, the process must then be carefully practiced.
Against this background, there is an increased demand to stably provide a relatively inexpensive photoelectromotive force member having a photoelectric conversion layer of large area and composed of an a-Si material which has a good uniformity and many practically applicable characteristics and which is suited for its particular application.
Conseguently there is an earnest desire to develop an appropriate method and apparatus to satisfactorily meet the above demand.
Likewise, there is a similar situation which exists with respect to other kinds of non-monocrystalline semiconducting layers which may constitute the photoelectric conversion layer of a photoelectromotive force member, for example, those composed of an a-Si material containing at least one selected from oxygen atoms, carbon atoms, and nitrogen atoms.